“Sometimes it is necessary to have some type of preliminary clearance in order to fill a slot,” the US director of national intelligence said in response to a question from Democratic New Mexico Senator Martin Heinrich.

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The 37-year-old is reportedly operating on an interim security clearance

“But if that is the case the access has to be limited in terms of the kind of information they can be in a position to receive.”

He told the Senate Intelligence Committee on Tuesday there is currently a government-wide backlog of 700,000 security clearance applications.

“The process is broken, it needs to be reformed. It’s not evolution, it’s revolution,” he said.

White House spokeswoman Sarah Sanders would not confirm the number of staff members who are operating with interim clearances.

“We are following a process that has been used by previous administrations and we would rely on the law enforcement and intelligence communities to determine if that process should be changed,” Mrs Sanders said during Tuesday’s news briefing.

Mr Coats’ testimony comes amid controversy over the interim security clearance granted to Mr Porter, the former White House staff secretary who was forced out last week after two ex-wives told US media he was emotionally and physically abusive to them.

The White House is also facing questions about presidential adviser Mr Kushner’s access to classified material.

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White House Chief of Staff John Kelly (L) has come under fire for defending Rob Porter (R)

Despite his lack of a full security clearance, Mr Kushner is able to read the President’s Daily Brief, a top secret intelligence report that Mr Trump himself does not bother to read, according to reports.